One of the more serious issues in medical practice is the compatibility of blood transfusions between patients. Transfusion of incompatible blood can cause a hemolytic transfusion event also known as intravascular hemolysis.
Intravascular hemolysis consists of the destruction of red blood cells (RBCs) due to the rupture of the RBC membrane and the liberation of the cell's contents into the peripheral blood circulation. Free hemoglobin is observed in the plasma (hemoglobinemia) and urine (hemoglobinuria) and renal function is often impaired due to red cell membrane fragments blocking the renal tubules. If not treated quickly, this blockage can lead to the loss of renal function and death.
Hemolysis is triggered by activation of the immune system following a transfusion due to the presence of antibodies in the patient's blood that promote the attack of the transfused RBCs. In most blood-typing systems, individuals within a group do not carry the antibody for which the group is named. Accordingly, these patients should be able to receive blood from similarly typed individuals without triggering hemolysis. In some situations, however, individuals within a group can develop the antibodies that they are believed to lack. Such antibody development can occur following a previous blood transfusion, multiple pregnancies, certain infections or by natural exposure to proteins that are homologous to human blood group antigens. For example, studies have shown that approximately 1-2% of all transfused patients produce a specific alloantibody to a blood group antigen. These figures are much higher among multiply transfused patients, such as sickle cell anemia or leukemia patients, that develop an array of antibodies making the determination of blood transfusion compatibility much more difficult.
Every sensitized person who has produced an antibody that is considered to be clinically significant must receive crossmatch-compatible blood. Cross-match compatibility is determined by mixing donor blood with the serum or plasma of the recipient and observing whether hemagglutination or hemolysis occurs. If either occurs, the blood is not transfused because of the possibility of causing a significant hemolytic event. Donor blood that is transfused must also be compatible with the recipient, and ideally shown to be antigen negative by testing with specific antisera. Thus, two tests are performed to increase the safety of the pending blood transfusion.
Presently available serologic tests can only identify the presence of RBC-specific antibodies in human sera. These assays cannot predict the probability of antibody-mediated hemolysis occurring during transfusion with any degree of certainty because they are not biologic assays.
The risk of a patient having a hemolytic event following transfusion is also evaluated partially based on historical data of that antibody specificity and what type of reaction it has been documented to cause. In very complex cases, a physician may have to weigh the consequences of transfusing incompatible blood with the survival of the recipient. Accordingly, improvement in blood compatibility testing is needed.